Printing heads for ink jet printers, which are known, operate in such a manner that liquid from at least one pump chamber is conducted through a corresponding number of outlet channels to a capillary tube located at the end of the respective channel. In these constructions one wall of the pump chamber is in the form of a diaphragm which is acted upon by means of a piezoelectric crystal in order to generate the necessary pumping action. Consequently, when voltage is applied to the piezoelectric crystal the diaphragm curves inwardly and the increased pressure in the pump chamber is projected through the respective channel to the capillary tube. This pressure causes a liquid drop to be ejected from the capillary tube at a great velocity, and on to a recording medium, for example, a sheet of paper.
It will be apparent that the shape and location of the capillary tubes are of great importance for the reliable operation of the ink jet printer. The capillary tubes used in this type of apparatus generally has a diameter in the order of 0.1 mm. Therefore, in order to print a written line which is easily legible, the capillary tubes must be arranged in close proximity to each other and in precisely defined places. In this regard, one should be aware of the fact that only a slight displacement of one capillary tube relative to the others will cause distortion of the printed line and make reading very difficult if not impossible.
It is evident that great accuracy in the manufacturing of ink jet printers is of utmost necessity. Up until the present time these capillary tubes have been produced by either etching, stamping or milling grooves in one flat plate which is then combined with another plate to cover the resulting grooves to thereby form capillary tubes.
Another known method of manufacture of printing heads for ink jet printers is to drill the tubes from an outer surface of the head inwardly to the respective channels. It should be apparent that in this method as well as in the other known methods of this type the requirement for accuracy is extremely high which causes the methods employed to be time consuming, expensive, and not suitable for mass production. In addition, by using this known method there is always a discontinuity in the location where the capillary tube passes into the channel, and this affects the function of the print head in an unfavorable manner, particularly after an ink drop has been delivered with the resulting retraction of the ink.